Lawrence Berkeley National Laboratory

The quasi-one-dimensional linear chain compound HfTe3 is experimentally and theoretically explored in the few- to single-chain limit. Confining the material within the hollow core of carbon nanotubes allows isolation of the chains and prevents the rapid oxidation which plagues even bulk HfTe3. High-resolution transmission electron microscopy combined with density functional theory calculations reveals that, once the triple-chain limit is reached, the normally parallel chains spiral about each other, and simultaneously a short-wavelength trigonal antiprismatic rocking distortion occurs that opens a significant energy gap. This results in a size-driven metal-insulator transition.